This in to the field of biologically active water purification systems using combinations of plants and microbial action, and to the physical construction of same.
It is known that biological pollution control systems can be of great effectiveness in purifying organic wastes within water. Typical systems are described in, for example, Wolverton, U.S. Pat. No. 4,959,084 disclosing an air pollution treatment facility flowing air through a waste water fluid and then flowing the combined fluid and pollutants through a combination of rocks, plants and microbes for purification.
One typical plant known to be of special effectiveness in converting and reducing organic contaminants in water go by the typical name of duckweed, a small floating aquatic plant usually found in mixtures of three Genera: Spirodela, Lemna, and Wolffia. Such plants are known to be extremely small floating upon the surface of the water and at a distance look like algae. Since they are not rooted into soil, various devices have been developed to promote and produce a uniform floating coat of these plants on a treatment pond. Typical ones are shown in U.S. Pat. No. 4,536,988 to Hogan disclosing a floating containment barrier grid structure for containing duckweed.
The general field of treatment of waste waters include U.S. Pat. No. 4,522,722 to Nicholas disclosing subsequential treatment first and anaerobic zone and then flowing the treated liquid through an aerobic zone producing sequentially reduction and oxidation as a method of removing sludge and in dealing with the retained nitrogen and phosphorus in the resulting water.
U.S. Pat. No. 4,209,388 to DeFraites discloses a sewage treatment method in which sequential ponds are gravity fed from a first pond containing algae for aerobic composition followed by a second pool for removal of the algae and a third "polishing" pond which provides an oxidation state.
U.S. Pat. No. 4,333,837 to Plosz, et al discloses a structure and apparatus providing for flow path water, one aquatic plant region and Wolverton, U.S. Pat. No. 4,415,450 disclosing sequential steps of subjecting the waste water to an anaerobic settling step passing the liquid through an anaerobic filter cell once it percolates up to an aerobic treatment stage.
U.S. Pat. No. 4,793,929 to Kikuth discloses a two-stage treatment process and summarizes advances pass the classic activated sludge process for treatment of sewage.